The present invention relates to an opto-electronic device and in particular a high speed photodetector having a semiconductor window layer which is substantially transparent to the intended signal and further having a beveled detector edge which functions to direct incident photons to the device's junction region.
Optical communication systems require high speed photodetection. This requirement is best exemplified in semiconductor laser operations where photodetectors must respond to light modulations on the order of nanoseconds. Transport properties, inherent to the particular semiconductor material used, have heretofore generally limited the speed of the detector. The photodetector of the present invention minimizes inherent materials limitations in providing a novel photodetector arrangement to optimize the response of the detector for a given set of semiconductor absorbtion and transport properties.
Of equal importance is the photodetector's design which facilitates automated production and/or assembly of the device and its related optical components. Present optical communications technology generally employs subminiature devices and near future chip integration of entire optical systems is evident. The photodetector of the present invention is adapted to facilitate coplanar construction of such assemblies.
Photodetectors known in the art are generally characterizable as comprising one of two configurations. Referring momentarily to the drawings, FIG. 1 illustrates the two general configurations for photodetectors known in the art. The configuration generally designated 10 has a major surface area designated 12 for receiving illumination. The principal drawbacks of this configuration involves the required positioning of the detector in perpendicular relationship with the light source's substrate which virtually prohibits coplanar positioning of the detector and light source. A secondary drawback involves the absorbtion characteristics of the junction forming layer. Thick junction forming layers capable of absorbing sufficient light increases the transit time of photon generated carriers correspondingly increasing the response time of the device.
The detector arrangement of the present invention is of further advantage as eliminating the need for additional passivation layers to reduce surface recombination.
The prior art detector generally designated 20 is readily adaptable to chip integration construction techniques; however, this configuration generally absorbs light distant from the device junction, relying on carrier diffusion which reduces the speed of the device.
Both prior art detector configurations are of further disadvantage in permitting substantial reflection from the surface of the detector, which in instances may coherently add to the laser light signal providing unwanted second mode signals.